2615
Inorg. Chem. 1985, 24, 26 15-2624
Contribution from the Department of Chemistry, McMaster University, Hamilton, Ontario, L8S 4M 1 Canada
Preparation and Multinuclear Magnetic Resonance Study of the Zintl Anions HgChzZ-, CdChZ2-,SnCh32-,TICh3>, SnCh4“-,and T12Ch22-(Ch = Se and/or Te). Chemical Shift and Coupling Constant Correlations ROBERT C. BURNS,*Ia LESLEY A. DEVEREUX, PIERRE GRANGER,lb and GARY J. SCHROBILGEN* Received August 14, I984
Multinuclear magnetic resonance spectroscopy is ideally suited to the study of the solution chemistry and structures of Zintl anions, as every post-transitionmetalelement forming a Zintl phase possesses at least one natural-abundance isotope.that is NMR active, many of which are spin nuclei. In the present work several new series of classical anions have been prepared and characterized by multinuclear magnetic resonance, while in other cases previously unreported examples of other series for which isolated examples were already known have also been characterized. All of the anions have been obtained by extraction of the appropriate ternary or quaternary Zintl phases of the type KM(Te/Se) or NaM(Te/Se), where M = Hg, Cd, TI, or Sn, with ethylenediamineor liquid ammonia in the presence of 2,2,2-crypt. These studies include (1) the linear HgCh?- (Ch = Se and/or Te) and CdCh22-anions, (2) the trigonal-planar TIChe3-and SnChe2-anions, (3) the tetrahedral SnCh,& anions, and (4)the cyclic TI2Ch?- anions, which are presumed to have the same ‘butterfly”-shaped geometry known for Tl2Te?-. All of these anions have been fully characterized in ethylenediamine or liquid-ammonia solutions by 203*205Tl, 199Hg,IZ5Te,Il9Sn, Il3Cd, and ”Se NMR spectroscopy. Relevant chemical shifts are reported and their trends discussed. An abundance of heavy-element spin-spin couplings are also reported, enabling structural comparison to be made within and betweeen series after the nuclear dependence has been removed (to give reduced coupling constants), and allowances have been made for relativistic effects, of major importance in the species studied. Introduction
Many of the heavy main-group elements form intermetallic phases (Zintl phases) with the alkali metals that give soluble products in liquid NH, or ethylenediamine (en). About 50 years ago, Zintl and co-workers24 described electrochemical studies on solutions of such sodium alloys together with the results of exhaustive alloy extractions. The homopolyatomic anions Sn9&, Pb94-, Bi73-, Sb73-, and Te42-were among the first species to be identified. However, any attempt to isolate these anionic species by evaporation of the solvent resulted in the formation of amorphous products or reversion to a known binary alloy phase(s) in the particular system. The macrobicyclic ligand 2,2,2-crypt5 has been successfully used to complex the alkali-metal counterion (Na+ or K+) in these solutions. This prevents the formation of other more stable intermetallic phases on removal of the solvent and generally increases the solubility of the anion(s) in the above solvents. The 2,2,2-crypt ligand contains a three-dimensional intramolecular cavity lined with six oxygen and two nitrogen binding sites and forms inclusion complexes in which the alkali metal is contained inside the molecular cavity. The use of cryptating agents has led to the stabilization and X-ray crystallographic characterization of a variety of novel homoplyatomic Sns2- (D3h) anions of widely varying geometries, i.e. Snge (C40),6 and PbS2-( 0 3 h ) , 7 Ge92- (D3h)and Ge94- (C40),8 Sb73- (C3u),9 and AsIl3- (D3).10 Mixed-metal anionic systems are also known. Elements like mercury and thallium, with their relatively low number of valence electrons, can be combined with less electropositive, more electron-rich elements to give heteropolyatomic species such as the tricapped trigonal-prismatic T1SnS3-and the bicapped squareantiprismatic T1Sn93- clusters,” the butterfly-shaped TlzTe22anion,12and the linear HgTe2- anion.I3 Heteropolyatomic anions
in which all elements are relatively electron rich have likewise been characterized, including the tetrahedral Sn2Biz2-and Pb2Sb22s p e c i e ~ , l and ~ ~ ’the ~ As2Se62-anion, which consists of a six-membered ring in a chair conformation with two exocyclic selenium atoms attached to the two opposed arsenic atoms in the ring.16 The use of multinuclear magnetic resonance spectroscopy is particularly suited to the study of the solution chemistry and structures of Zintl anions, as every post-transition-metal element forming a Zintl phase possesses at least one natural abundance isotope that is N M R active. A large number of these elements possess naturally occurring isotopes that are spin 1/2 (nonquadrupolar) nuclei and are capable of providing additional valuable structural information based upon their hetero- and homonuclear spin-spin couplings.17 Previous studies by Rudolph and co-workers of the Nal,2Sn, NaSnlz5, NaSnPb, NaGeSn, KGeSn, and NaSnT1, alloy extracts in en and liquid N H 3 in the absence of a cryptating agent have led to the characterization of Sn42-, Sn94-,Pb94-, and the mixed-metal anions Sn+,,Pb,,& (n = 1-8), Sn+,Ge,4- (n = 1-8), and TISng5-in solution by II9Sn and 207PbN M R spectroscopy.’8-20 Interestingly, all of the nine-atom species have been found to be fluxional on the N M R time scale, and this therefore underscores the importance of multinuclear magnetic resonance spectroscopy as a complementary structural tool to X-ray crystallography in the study of these species. Much of the early work on Zintl anions and work until the present have produced cluster, cage, or ring cluster species. It is only recently that a few examples of heteroatomic classically bonded anions extracted from Zintl alloys have come to light. These include the aforementioned HgTe2- anion, while extraction of an NaSnTe alloy in en has led to the formation of SnTe44-,20 which recently has been shown to have a tetrahedral structure ~
(1)
Present address: (a) 41 Stanley St., Blackrock, Victoria 3193, Australia;
(b) Departement de Chimie, IUT de Rouen, 76130 Mont-Saint-Aignan,
France. (2) Zintl, E.; Goubeau, J.; Dullenkopf, W. Z . Phys. Chem. Abt. A , 1931, 154, 1 .
(3) Zintl, E.; Harder, A. Z . Phys. Chem., Abt. A 1931, 154, 47. (4) Zintl, E.; Dullenkopf, W. 2.Phys. %hem., Abt. B, 1932, 16, 183. (5) Lehn, J. M. Ace. Chem. Res. 1978, 11, 49. (6) Corbett, J. D.; Edwards, P. J . Am. Chem. SOC.1977, 99, 3313. (7) Edwards, P.; Corbett, J. D. Inorg. Chem. 1977, 16, 903. (8) Belin, C. H. E.; Corbett, J. D.; Cisar, A. J. Am. Chem. SOC.1977, 99, 7163. (9) Adophson, D. G.; Corbett, J. D.; Merryman, D. J. J. Am. Chem. SOC. 1976, 98, 7234. (10) Belin, C. H. E. J. Am. Chem. SOC.1980, 102, 6036. (11) Burns, R. C.; Corbett, J. D. J. A m . Chem. SOC.1982, 104, 2808.
~~
~
~~
~~
(12) Burns, R. C.; Corbktt, J. DIJ. Am. Chem. SOC.1981, 103, 2627. (13) Burns, R. C.; Corbett, J. D. Inorg. Chem. 1981, 20, 4433. (14) Critchlow, S. C.; Corbett, J. D. Inorg. Chem. 1982, 21, 3286. (15) Corbett, J. D.; Critchlow, S. C.; Burns, R. C. “Rings, Clusters and Polymers of the Main Group Elements”; Cowley, A. H., Ed.; American Chemical Society: Washington, DC, 1983; ACS Symp. Ser. No. 232, Chapter 6, p 95. (16) Berlin, C. H. E.; Charbonnel, M. M. Inorg. Chem. 1982, 21, 2504. ( 1 7) Harris, R. K. In “NMR and the Periodic Table”; Harris, R. K., Mann, B. E., Eds.; Academic Press: London, 1978; Chapter 1, p 1 . (18) Rudolph, R.; Wilson, W. L.; Parker, F.; Taylor, R. C.; Young, D. C. J . A m . Chem. SOC.1978, 100, 4629. (19) Rudolph, R. W.; Taylor, R. C.; Young, D. C. “Fundamental Research in Homogeneous Catalysis”; Tsutsui, M., Ed.; Plenum Press: New York, 1979; p 997. (20) Rudolph, R.; Wilson, W. L.; Taylor, R. C. J . Am. Chem. SOC.1981, 103, 2480.
0020-1669/85/1324-2615$01.50/0 0 1985 American Chemical Society
2616 Inorganic Chemistry, Vol. 24, No. 17, 1985
Burns et al.
'
Table I. NMR Parameters for the HgCh?- Anions chem shift, 8 coupling const J , Hz
Hg obsd calcd '91
I
2WOHr
A
1 2 5 ~ ~ 71se
anion obsd obsd HgTe22- -2169 -2180 -726.4 HgTeSe2- -1516 -1494 -889.4 -30.5 HgSe2-796 807 -142.27
lzsTe 6500 6470
77Se 2270 2258
in the Zintl phase Na4SnTe4.2' In the present work, we have sought to investigate and to extend the range of known classically bonded heteropolyatomic anions of the immediate post-transition-metal and main-group elements, using multinuclear magnetic resonance spectroscopy as the primary tool for their identification. The synthetic rationale used here was to stabilize Zintl anions containing the (relatively) valence-electron-poor elements by preparing mixed species having a significant number of very electron-rich atoms, namely selenium and/or tellurium, which are fairly easily reduced and as such can effectively act as pseudohalogens (Le., Se- or Te- are isovalent with a halogen atom), thus allowing the central metal atom to become extensively coordinated. Results and Discussion The experimental approach involved the syntheses of ternary or quaternary alloys of the type M-X-Te, M-X-Se, and M-XTe-Se where M = alklai metal ( N a or K) and X = Hg, Cd, Sn, or Tl. The resulting Zintl phases were extracted in a suitably basic solvent, en or liquid NH3, always in the presence of 2,2,2-crypt, and the resulting solutions investigated by multinuclear magnetic resonance spectroscopy. In all cases residual solid remained after extraction, but these residues were not investigated in view of the lack of data concerning the appropriate ternary or quaternary systems except to note that the majority were, like the initial alloy compositions themselves, hydrolytically unstable. Identification of the Zintl anions observed in this study was dependent upon correct N M R assignments.. The reliability of the assignments was assured by a combination of two or more of the following criteria: (1) distinctive heteronuclear N M R coupling patterns arising from isotopically dilute spin nuclides (see Supplementary Material for a table of observed and theoretical satellite intensities); (2) isotopic enrichment in either 77Seor lZ5Te to give the appropriate spin multiplicities corresponding to the number of ligands; (3) identification and consistent behavior of peaks from the same species in the spectra of two or more nuclei; (4) systematic variation of the relative intensities of species as the ratio of tellurium to selenium was changed; ( 5 ) for the tincontaining species, corroboration of the N M R assignments by lI9Sn Mbsbauer spectroscopy. Mbsbauer studies on the anions studied in this work and on related systems have been reported in a previous paper.22 In addition, the N M R assignments have been found to be consistent with empirical and periodic trends noted throughout the course of this work. (I) Zintl Anions Extracted from KHgTe, KHgSe, and KHgTe&e,,5 Alloys. The only member of the HgCh2- series known prior to this work was HgTe?-. This anion has been characterized by a single-crystal X-ray study and shown to possess a linear geometry (Dmhsymmetry).I3 Extraction of the alloy KHgTe in en in the presence of 2,2,2crypt gave a deep yellow solution as previously noted,I3 while extraction of KHgTeo,5Seo,5and KHgSe gave progressively paler solutions. The entire series of HgChz2-anions was identified and characterized by obtaining the natural-abundance lwHg (16.84%), lZ5Te(6.99%), and 77Se(7.58%) N M R spectra of these extracts. The assignments are unambiguous as only one species was observed for each of the ternary alloy systems and all three species were observed in the extract from the quaternary alloy system. Assignments were confirmed, as indicated above, by observation of satellite doublets of appropriate intensity arising from one-bond ~~
~
(21) Eisenmann, B.; Schifer, H.; Schrod, H. 2. Nuturforsch.,E Anorg. Chem., Org. Chem. 1983, 388, 921. (22) Krebs, B.;Hinter, H.-U. Z . Anorg. Allg. Chem. 1980, 462, 143.
I - 700
I
I
-900
-800
8,%1
ppm
i
fran ICH,),
W H z
HQ)
' B
I
b ' &ofi
'
'
1760.
I
' i7;O
1
:e60
b,,,(ppm
'
-ab'
-&'
-950
from (CH,),TO)
Figure 1. (a) 199HgNMR spectrum, obtained at 44.80 MHz, for the HgSe22: (A) anion. Peaks labeled a denote 77Sesatellites. (b) 125Te NMR spectrum of the HgCh22-series of anions, obtained at 78.92 MHz: (A) HgTe*-; (B) HgTeSe". Peaks labeled a and b denote 199Hgsatellites. Table 11. NMR Parameters for the CdCh? Anions
CdTe22- -487.7 (-500.2). CdTeSe2- -343.3 (-347.8) CdSe2-69.0 (-69.1)
-1159.0
2148 (2203)
2058
"Data recorded for CdCh2- in liquid NH, is given in parentheses. 199Hg-77Seand 199Hg-125Te couplings in the N M R spectra of each pair of coupled nuclei (Figure 1). The chemical shifts and coupling constants for the series of HgCh2- anions are listed in Table I, and it may be noted that the Ig9Hgchemical shifts are additive in nature. Trends among chemical shifts and coupling constants will be summarized in a later section. (11) Zintl Anions Extracted from KCdTe, KCdSe, and KCdTeo.sSeo.5 Alloys. With the preparation and characterization of the HgCh2- series of anions, it seemed likely that the analogous, but unknown, cadmium species should exist. Accordingly, the alloys KCdTe, KCdTeo,5Seo,S,and KCdSe were prepared and extracted as for the corresponding mercury alloys, giving yellow-orange, yellow, and pale yellow solutions, respectively. Examination of these extracts by natural-abundance lI3Cd (12.26%), 125Te,and 77Se N M R provided evidence for a new series of CdCh2- anions by analogy with the related mercury system on the basis of the same criteria. However, while all chemical shift and coupling constant data were obtained for CdTe?-, the CdSe2and CdTeSeZ-anions were not soluble enough to enable other than l13Cd chemical shift data to be recorded. Similar results were obtained when liquid N H 3 was used as the solvent. All data are listed in Table 11, and, interestingly, the '13Cd chemical shifts do not exhibit the highly additive nature exhibited by the lg9Hg chemical shifts of the related HgChZ2-series of anions. As for the HgCh3- series of anions, the CdCh2- anions are each assumed to have a linear geometry like that of HgTe22-.'3 (III) Zmtl Anions Extracted from KSnTe2-$e, (x = 0, 3/2, 2) and NaSnTe,$3ex (x = 0, 2/3, 1) Alloys. In view of the fact that Rudolph and co-workersZ0had already observed the II9Sn and lz5TeN M R spectra of SnTe4' and the crystal structures of Na4SnTe4and Na4SnSe4-16 H 2 0 have recently been two tin-containing ternary alloys were prepared, one tellurium
Classical Zintl Anions
Inorganic Chemistry, Vol. 24, No. 17. 1985 2617 C 2000 Hz M I
8 D
C', ,C"
J
I
8
I
i i l
-5x)
e
.
l
-5x)
.
l
-540 $s,(P~
.
l
,
l
-550 -560 from (CH,),Sn)
.
-570
l
.
l
~
-580
Figure 2. (a) Il9Sn NMR spectrum of the SnTet- (A) anion, obtained at 93.27 MHz. Peaks labeled a' denote I2'Te satellites; peaks labeled a" denote I 2 q e satellites. (b) I2-'TeNMR spectrum, obtained at 78.92 MHz, for the SnCh,> series of anions. The peak assignments are as follows: (A) SnTe32-; (B) SnTe2Se"; (C) SnTeSe?-. Peaks labeled a', b', and c' denote "9Sn satellites while those labeled a", b", and c" denote Il7Sn satellites. (c) 77Se NMR spectrum for the SnCht- series of anions, obtained at 47.70 MHz: (A) SnTe2Se2-;(B) SnTeSel-; (C) SnSe,*-; (D) unknown resonance. Peaks labeled c' and c" denote II9Sn and "'Sn satellites, respectively; (d) II9SnNMR spectrum of the SnTe2Se2-anion, obtained at 93.27 MHz. Peaks labeled a' denote 77Sesatellites; oeaks labeled a" denote I2'Te satellites. (e) 119SnNMR spectrum of the SnTeSel- anion, obtained at 93.27 MHz. Peaks labeled a' denote 77Sesatellites; peaks labeled a" denote '25Tesatellites
rich, the other selenium rich, with the view in mind to observe the SnSebnTenC (n = 0-4) series of anions. An alloy of composition KSnTeo,SSel,syielded a deep amber solution when extracted with en in the presence of 2,2,2-crypt, while an alloy of composition KSnTel,Se0,, produced a reddish-orange solution similar to that of Sn9&under the same conditions. These solutions were investigated by Il9Sn (8.58% natural abundance), lZ5Te,and 77SeN M R spectroscopy. A series containing five tetrahedral SnCh4&anions was expected. Evidence for only four species in solution was, however, obtained. Efforts to find low concentrations of the Sn9&, SnTe4&, and (see below) SnSe4&anions in the II9Sn N M R spectra of these solutions provided no evidence for their presence. Rather, the signals have been assigned to a new series of classical, triply coordinated anions, viz. SnTe3", SnTezSe2-, SnTeSez2-, and SnSe3z-. The assigned formal charge of 2- for these anions has been deduced from "??in Mijssbauer spectroscopy on the basis of oxidation state considerations and is discussed in a subsequent section. Members of this series therefore possess 24 valence electrons and thus are isovalent with the C032-anion. Not unexpectedly, extraction of the ternary alloys KSnTe, and KSnSez under the same conditions gave the pure SnTe;- and SnSe32-anions, respectively. Again, no evidence could be found for the presence of the SnTe4& or SnSe4&anions in these alloy extracts. SOcb3,- (Cn = Te and/or Se). The assignments of the SnCh3species were accomplished by obtaining the l19Sn, lZsTe,and 77Se
spectra of each new SnCh32-anion (Figure 2). In every case, natural-abundance satellite doublets were observed as a result of directly bonded spin-spin coupling between the spin 1/2 nuclei, i.e. 119Sn-125Te,117Sn-1ZsTe,119Sn-77Se,and 117Sn-77Se(natural abundance of l17Sn, 7.61%). The observations of natural-abundance satellite spectra enabled unambiguous assignments to be made on the basis of the following considerations: (i) 117J19SnlzsTecouplings are always larger in a homologous series than 117J19Sn-77Se couplings by virtue of the larger magnetogyric ratio (ii) the spin-spin couplings could be of lzsTe relative to 77Se;17 observed in the spectra of each pair of spin-coupled nuclei; (iii) relative satellite intensities in the Il9Sn spectra confirmed the assignments of (a) SnT%Se2- and SnTeSe:-, as the 12?e satellites in SnTezSeZ-should be approximately twice the intensity of the more closely spaced 77Sesatellites while the opposite intensity distribution is expected for S n T e S e P (Figure 2d,e), and (b) every member of the series by comparison of the integrated intensities of each satellite doublet with those calculated from the percent natural abundances of the ligand atoms. The relevant chemical shifts, coupling constants, and assignments for the SnCh3- series of anions are given in Table 111. All of the lI9Sn, lZsTe,and 77SeN M R assignments are supported by good agreement of the observed chemical shifts with those calculated from a least-squares linear regression analysis of the data, which is discussed in a later section. From Table I11 it is also apparent that not only are the chemical shifts additive in nature
2618 Inorganic Chemistry, Vol. 24, No. 17, 1985
Burns et al.
Table 111. NMR Parameters for the SnCh32-Anions chem shift, 6
SnTee2-" -1 170.1 SnTe2Se2-853.1 SnTeSe22-b -548.7 SnSe32-264.3 'Jl'9sn-123Te
-1 162.4 -860.2 -558.0 -255.8
= 3776 Hz.bJ12'T,77%
-385.2 -499.5 -625.0
-383.3 -503.2 -623.1
46.67 -19.52 -92.16
47.75 -21.67 -91.09
99.6 49.4 -5.8 -61.9
101.3 47.3 -6.7 -60.6
4535 4792 5035
4335 4577 4816
1916 1996 2051
1923 1959
1264 1341 1402 1463
1282 1342 1398
= 79.4 Hz.
Table IV. NMR Parameters for the SnCh4&Anions chem shift. 6
SnTe2SnTe3Se4SnTe Se 4SnT&ejSnSe,'
-1823.6 -1472.3 -1 124.8 -791.9 -476.6
-1812.7 -1475.3 -1 137.8 -800.4 -463.0
-203.3 -293.4 -395.1 -499.4
-199.3 -298.3 -397.3 -496.3
but the spinspin coupling constants are also directly additive. Trends concerning the chemical shifts and coupling constants are discussed in a subsequent section. Miksbauer Studies. From the relevant N M R satellite intensities and the number of species present, it has already been demonstrated that the central tin atom is triply coordinated in solutions extracted from the KSnTe,, KSnSe2, and KSnTe2,Se, (x = 0, 112,3/2, 2) alloys. There are, however, two possible triply coordinated structures that are consistent with these findings. The first is a trigonal-pyramidal structure (I) with a lone pair on tin
.. I
4-
Ch
2-
I1
so that tin possesses a formal oxidation state of +2, Le. SnCh3&, while the second is a trigonal-planar structure (11) where tin has a formal oxidation state of +4, i.e. SnCh?-. As Sn(I1) and Sn(1V) compounds normally give characteristic and well-defined Il9Sn Mijssbauer isomer samples of SnTe3" and SnSe3" as well as the mixed anions were prepared in order to resolve the above ambiguity and to allow assignment of the actual charge on these anions. The Mossbauer parameters of the various species studied in this work are discussed in detail elsewhere.24 Importantly, it should be noted here that all isomer shift values for the above 1.6-1.8 mm s-l) were characteristic of tin in the +4 samples (a. oxidation state whereas Sn(I1) resonances are found above that of a&, 2.02 mm s-1.25 SnCh4& (Ch = Se and/or Te). The two tetrahedral species, SnTe4' and SnSe44-,were prepared by extracting the alloys NaSnTe and NaSnSe with en in the presence of 2,2,2-crypt, while solutions containing the mixed species were obtained by extraction and NaSnTe, 33se0.67, of the quaternary alloys, NaSnTe, 67Seo.33 under the same conditions. The chemical shifts and coupling constants for all species are summarized in Table IV and confirm that neither SnTe44- nor SnSe4& was present in the original K-Sn-Te-Se studies, which led to the formation of the trigonal-planar species. The Il9Sn chemical shift and 119Sn-12sTe coupling constant of SnTe4&agree with those previously reported by Rudolph and co-workers,2° but the lZ5Techemical shift quoted by them (-604.4 ppm) differs by almost 400 ppm from our value of -212.4 ppm. After the acquisition parameters were rechecked, one can only conclude that there is a referencing problem asso(23) Greenwood, N. N.;Gibb, T. C. 'Miissbauer Spectroscopy"; Chapman and Hall Ltd.: London, 1971; p 371. (24) Birchall, T.; Burns, R. C.; Devereux, L. A,; Schrobilgen, G. J. Inorg. Chem. 1985, 24, 890. ( 2 5 ) Stevens, J. G. Hyperfine Interact. 1983, 13, 221.
3119 3340 3571
2981 3192 3418
ciated with the literature result and that the value for the 125Te chemical shift reported in the present work is in fact the correct value. Like the trigonal-planar series of anions, SnCh32-, the chemical shifts of the tetrahedral SnCh44-anions can be fitted by using a least-squares linear regression analysis, and it is also evident from Table IV that the chemical shifts are additive in nature as well as the spinspin coupling constants. Again, trends among these parameters are dealt with in a later section. At least two additional species were observed in the 125Te spectrum of the extract of NaSnTe (-436 ppm, -619 ppm), but they have not been thoroughly investigated as of yet. Although no positive assignments can be made at this time, possible candidates include species like and Sn2Te64-,analogous to the known M2Ch$- and M2Ch64-anions, where M = Ge or Sn and Ch = S or Se.26 At this point it is instructive to speculate on the differences observed on extraction of the alloys NaSnCh and KSnCh, (Ch = chalcogen), which gave the SnCh44-and SnCh32-species, respectively. In the former, Sn is nominally Sn(I), i.e. Na+Sn+(Ch2-), while in the latter it is nominally Sn(III), i.e. K+Sn3+(Ch2-)2. Disproportionation of the Sn(1) or Sn(1II) in each case can be represented by
4Sn+
-
4Sn3+
-
+ 3Sn 3Sn4+ + S n
Sn4+
This leads to ratios of Ch2-/Sn4+of 4 and 2.67 (-3), in agreement with the products obtained and with the observation that there was no evidence for SnCh3,- species in the extraction of the NaSnCh alloys or SnCh:species on extraction of the KSnCh, alloys. (IV) Zintl Anions Extracted from KTITe, KTISe, and KTIT~,sSe,-,sAlloys. The only simple heteroatomic ring derived from a Zintl alloy is TlzTe?-, the structure of which has been previously determined by X-ray crystallography.I2 In the hope of producing the mixed T12TeSe2-and T1,Se2,- anions, alloys of composition KTlTe&3% and KTlSe were prepared in addition to KTlTe, from which T12Te2,- has been obtained. In each case, deep reddishbrown solutions resulted upon extraction with en in the presence of 2,2,2-crypt and were investigated by natural-abundance ,03TI (29.50%) and 205Tl(70.50%), IZ5Te,and 77SeN M R spectroscopy. As anticipated, evidence was obtained for the new anionic species, T12%2- and T12TeSe2-. However, it was immediately evident from the ,05Tl and 203Tlspectra that there were more species present than expected for the simple, mixed series T12Ch22-(Ch = Te and or Se . In order to obtain structural information based upon ,03* sTl 125Teand 203*205Tl-77Se spin multiplicities, two quaternary alloy samples, one containing enriched tellurium (77.3% 125Te)
zd 2
( 2 6 ) Krebs, B. Angew. Chem., Int. Ed. Engl. 1983, 22, 113.
Classical Zintl Anions
Inorganic Chemistry, Vol. 24, No. 17, 1985 2619 is neglected, then each signal would consist of a doublet of triplets (20sT1203T177Se22-) overlapping with a triplet (zo5T1277Se22-). However, because of the broad natural line width and the two-bond 205Tl-203Tlcoupling (5000 Hz) being about twice that of the zosT1-77Secoupling (2260 H Z ) - ~ J ~ O ~ ~is , similar, - V ~ ~ as noted above-no individual couplings were observed and a "pseudoquintet" occurred for both 2osTl and z03Tlsignals, the respective intensity patterns resulting from the different percentage abundances of the two thallium isotopes. The 20sT1and 203Tlresonances of the TlzTeSe2- anion obtained from the extract of the nonenriched quaternary alloy both consisted of broad ( A Y ~ , ~ 3000 Hz) singlets. This suggests that the two-bond 205T1303Tlcoupling for this anion is less than about lo00 Hz as no evidence of a coupling could be observed. Indeed, it could even be absent. The 2osTland 203Tlspectra obtained from the 77Se-enriched alloy extract both appear as doublets with a 203*20sT1-77Se coupling of 2100 Hz. It is apparent, particularly from the 203Tlspectrum (the less abundant thallium isotope) that the 205Tl-203Tlcoupling must be considerably less than 1000 Hz, with a maximum value of about 300 H z on the basis of a crude line-shape analysis of the 205Tland 203Tlsignals for T12TeSe2-and TlzSe22-,those of the latter providing a measure of the natural line width. The 2osTland 203TlN M R spectra from the extract of the 125Te-enrichedalloy appear as broad, three-line signals. The outer lines arise from a 203~zosT1-12sTe coupling of 3620 H z while the central line arises as a result of the contribution from an isotopic isomer containing spinless tellurium (and selenium). Although a small central peak would also have been expected in the enriched selenium case, the lower spinless abundance (5.6% vs. 22.7%), smaller coupling constant for selenium to thallium than for tellurium, and broad line width apparently combine to mask its presence. The appearance of the above spectra of Tl2TeSe2containing enriched lzsTeor 77Seare consistent with a two-bond 2osTl-203Tlcoupling constant of between 300 and 0 Hz. The 77Se N M R spectrum of the extract of the 77Se-enrichedalloy showed a broad 1:2:1 triplet (along with signals from the T1Ch:- species, see below) at about 414 ppm, with an apparent coupling of about 2150 Hz. Both the chemical shift and coupling constant are similar to those for Tl2Se?- (which is present in the sample), but no other signal appears that could be attributed to TlzTeSe2-. We therefore conclude that the 77Se resonances of Tl2SeZ2-and ~ Tl2Sez2-is 405 ppm, as Tl2TeSe2-are almost identical ( 1 3 7 7 ~for noted above), and this is supported by the observation that the apparent z03,20sT1-77Se coupling constant of the triplet, 2 150 Hz, is about midway in value between those of T12Se?- (2260 Hz) and T12TeSe2-(2100 Hz); note also that the 20STland 203T1N M R spectra show that there are about equal concentrations of these anions present in the sample. The lzsTe N M R spectrum of the extract of the lz5Te-enrichedalloy also exhibited a broad 1:2:1 triplet at -1 14.9 ppm with a 203~205T1-125Te coupling constant of 3610 Hz, in addition to signals from the TlCh33- species, which are discussed below. This coupling constant is in good agreement with that (3620 Hz) obtained from the 2osTland 203TlN M R spectra of the same extract, given above. We thus assign this triplet to the TlzTeSe2- anion. Like T12Sez2-,it is proposed that the Tl2TeSeZ-anion has the same butterfly-type geometry established for T12Te22-in the solid state.12 It is particularly interesting to note that no evidence was found for the existence of the T1zTe22-anion at room temperature in any of the solutions extracted from the enriched or naturalabundance quaternary KTITeo,SSeo,S alloys or in those resulting from the extraction of KTlTe by en or liquid NH, in the presence of 2,2,2-crypt, although it is from solutions of the latter type that the TI2Te?- anion was originally obtained as the solid compound (2,2,2-~rypt-K+)~Tl,Te?-*en. However, when a saturated liquid N H 3 solution obtained by extraction of KTlTe in the presence of 2,2,2-crypt is cooled to -40 OC, a 20sT1resonance was observed = 8006 Hz), at 8128 ppm with accompanying satellites (JZO~-,-I~S~~ which we attribute to the TlzTeZ2-anion. The chemical shift is comparable to those of T12Se22-and T1,TeSe2- and is consistent with the formation of T12Tez2-. Based on the line width, the two-bond 20sTl-203Tl coupling constant may be estimated to be
-
b
I 7800
1
1
7 m 8,,(ppm
1 1 7600 from O.IM aq. TIOAC)
1
7500
Figure 3. (a) 205Tland (b) 203TlNMR spectra of the Tl2SeZ2anion, obtained at 57.76 and 57.20 MHz, respectively. The spacing between lines B represents the 203Tl-205Tl spin-spin coupling.
and the other containing enriched selenium (94.4% 77Se) were prepared, extracted, and investigated to accurately determine the nature of the species present in the above solutions. This led to the identification of the TlCh33-series of anions, analogous to the SnCh2- series of anions discussed above. TlzCh?- (Ch = Te and/or Se). A single resonance at 7656 ppm from 0.1 M thallous acetate was observed in the z03T1and zosTl spectra from the resultant en extract of the ternary KTlSe alloy. Evidence for a two-bond 203Tl-20sTlcoupling was observed in the spectrum *05Tlspectrum (Figure 3a), and the corresponding 203T1 (Figure 3b) confirmed this 203T1305Tlcoupling, with a magnitude of 5000 Hz. The 77Sespectrum showed a triplet at 405.3 ppm from (CH3)2Sewith a 20sT1-77Sespinspin coupling of 2260 Hz (203T1-77Secoupling could not be resolved owing to a combination of three factors: broad natural line widths, lower natural abundance of 203Tl,and the very similar magnetogyric ratios of 203Tl and 205T117).The multiplicity pattern and the relative intensities of the peaks led to the assignment of this species as Tl2Se?-, which is presumed to possess the same solid-state butterfly geometry as reported for the T12Te22-anion.l* 2osTland 203TlN M R studies of the solution extracted from the nonenriched quaternary alloy KTlT%,5S%,Sindicated the presence of only two species in the high-frequency region of the spectra (7654 ppm and 7877 ppm from 0.1 M thallous acetate) which were assigned to the T12Se?- and T12TeSeZ-anions, respectively. N o evidence was obtained for the presence of TlzTezZ-,and this is discussed in greater detail below. The above signals occurred at essentially the same chemical shifts ( < f l ppm) for the extracts obtained from the lZsTe-and 77Seenriched alloys. As noted above, the solution extract from KTlSe gave a resonance a t 7656 ppm in both the 2osTland 203TlN M R spectra for Tl2SeZ2-,which is in good agreement with the former value. Again, 203Tl-205Tl couplings appear as satellite doublets in both the z03Tland zo5Tl N M R spectra, the relative intensities of which are in accord with our assignment of this signal as Tl2SeZ2-. This assignment was also confirmed by the observation of the 77Se spectrum, which exhibited the expected 1:2: 1 triplet due to 203,205T1-77Se coupling; again the individual 203T1-77Seand zo5T1-77Se couplings could not be resolved for the reasons given above. For the 77Se-enriched sample, the coupling patterns for the 20STland 203Tlresonances of Tl2Se2,-were more complicated as a result of the increased 77Se abundance. If the contribution involving spinless selenium (5.6%)
Burns et al.
2620 Inorganic Chemistry, Vol. 24, No. 17, 1985 Table V. N M R Parameters for the TlzCh2- Anions chem shift, d
anion
205T1
T12Te22-' T12TeSe2Tl2SeZ2-
8128 7877 1655
I2Te
77Se
205T1203Tl
-1 14.9
-414 405.3
